The present invention relates to a rubber member for paper-feeding machine parts as in copying machines, printers of computers, word processors and facsimile machines and the like. More particularly, the invention relates to a rubber member such as rubber rollers, rubber belts and the like used as a part of paper-feeding machines capable of very smoothly transferring paper sheets with an outstandingly high coefficient of friction against paper and excellent stability against variation in the ambient conditions and in the lapse of time.
The above mentioned machines for office automation each must have a mechanism for feeding and transfer of paper sheets which always includes a rubber member such as rubber rollers, rubber belts and the like coming into frictional contact with the paper sheet. It is readily understood that, in order to ensure good smoothness of feeding and transfer of paper sheets, the surface of the rubber member must have a high coefficient of friction with the paper sheet. In this regard, the rubbery material of the rubber member for paper-feeding machine parts is limited to several types of rubbers including so-called EPDM rubbers, i.e. copolymeric rubbers of ethylene, propylene and a diene monomer, polychloroprene rubbers, polynorbornene rubbers and the like among synthetic rubbers. Spongy or foamed bodies of these rubbers can also be used for the purpose though, naturally, with some decrease in the mechanical strength.
These known rubbers, however, are not always quite satisfactory as a material of a rubber member for paper-feeding machine parts in respect of their relatively poor performance under adverse ambient conditions. The rubbers heretofore used in such an application usually have a relatively low hardness of 15.degree. to 40.degree. Hs as determined according to JIS K 6301 in the scale A because a low hardness of the rubber is a favorable condition for smoothness of paper feeding by exhibiting a large deformation or so-called nip amount under a specified pressing load. Such a low hardness of a rubber article can be obtained only by compounding the rubber composition with a large amount of plasticizers or softening agents unavoidably to cause various troubles such as bleeding of the plasticizer or softening agent on the surface, decrease in the mechanical properties and weatherability, instability of the coefficient of friction in the lapse of time and so on. In the rubber rollers for automatic paper feeder in facsimile machines, in particular, the paper for printing is usually impregnated or treated with a silicone oil which necessarily migrates toward the surface of the rubber roller and is accumulated there resulting in gradual decrease of the coefficient of friction eventually not to ensure smoothness of paper transfer.
Alternatively, a proposal has been made for the use of a silicone rubber as a material of a rubber member for paper-feeding machine parts. Silicone rubbers are generally stable against adverse ambient conditions and have a capacity to absorb silicone oils without accumulation in the surface layer so that the above mentioned problems can be at least partly solved. Unfortunately, however, conventional silicone rubbers in general have a relatively low coefficient of friction not to ensure smoothness and stability of paper transfer and are subject to the changes of the surface condition by abrasive wearing in contact with paper sheets to cause a decrease in the performance for paper transfer.